Pressure relief system for paint circulation applications

ABSTRACT

A paint circulation system ( 10 ) for automotive coating applications presents a paint supply source ( 18 ) and a pump ( 20 ) for pumping the paint. A circulation line ( 16 ) is fluidly communicated with the paint supply source ( 18 ) and circulates the paint at an operational pressure. A relief line ( 28 ) has a pressure relief device ( 30 ) adaptable for withstanding a predetermined pressure of the paint and to circulate the paint through the relief line ( 28 ) as the operational pressure exceeds the predetermined flow pressure. A pressure control mechanism is operatively communicated with the circulation line ( 16 ) and the relief line ( 28 ). The pressure control mechanism senses the operational pressure to continuously circulate the paint in the relief line ( 28 ) in response to a difference between the operational pressure and the predetermined pressure before the operational pressure exceeds the predetermined pressure thereby preventing the pressure relief device ( 30 ) from actuating.

RELATED APPLICATION

This application claims priority to and all the benefits of U.S. Provisional Patent Application Ser. No. 60/533,660 filed on Dec. 31, 2003.

FIELD OF THE INVENTION

This invention relates to paint circulation systems used in automotive industry, and in particular, to a pressure control device for a paint circulation system.

BACKGROUND OF THE INVENTION

A production paint application process where paint is applied to a substrate, such as, for example a vehicle body moving through a paint booth, requires paint to be transferred from a paint reservoir to a paint applicator disposed in the paint booth. Due to the complex nature of most paint application facilities, wherein the paint booth is located, the reservoir is located a substantial distance from the paint applicator that atomizes and applies paint to the substrate of each vehicle body.

The layers of paint applied to each vehicle body generally include a spray primer surfacer, a spray base coat, and a clear coat. Each of these paints, and in particular, the spray primer surfacer and the base coat are necessarily maintained in continuous circulation to prevent the solids suspended in these paints from settling, which is known to cause paint defects that are visible in the painted products. Furthermore, colored primer surfaces and base coats generally include high percentages of pigment which are known to settle when these paints are not maintained in continuous circulation.

To transfer these paints from the paint reservoir to each paint applicator, the circulation system is installed in each paint facility, which may stretch across an expanse of hundreds of meters. These paint circulation systems include paint lines through which the paint is continuously circulated between the paint reservoir and a color changer, located just prior to each applicator, by a circulation pump. The paint lines generally include several valves intended to stop circulation through the paint line for maintenance operations. For example, most paint circulation systems include a bag filter that must be periodically replaced. To remove a typical bag filter, valves are located both upstream and downstream of the filter, each of which is closed during a filter change operation. This prevents paint from spilling during the filter change operation which would require hazardous waste cleanup.

It is necessary to terminate operation of the circulation pump prior to closing a valve downstream of the pump to prevent damaging of the pump or seals which prevent paint from leaking from the paint circulation system. For example, if the paint is prevented from circulating while the pump continues to operate pressure will build up in the paint line causing damage to various seals both inside and external to the pump, which again could cause paint to spill requiring a hazardous waste cleanup. To prevent this type of damage from occurring, a rupture disc type pressure relief is generally installed in a bypass loop of the paint circulation system, which is triggered at a predetermined pressure not when paint is prevented from circulating due to, for example, a closed valve. Once the rupture disc has ruptured, it must be replaced prior to reactivating the paint circulation pump and reinitiating production through the paint facility. This is known to be a laborious and slow process which results in significant amounts of lost production through the paint application facility.

Therefore, it would be desirable to provide a secondary relief to the paint circulation system that is triggered upon a predetermined pressure buildup within the paint circulation system thereby preventing the rupture disc from rupturing.

SUMMARY OF THE INVENTION

A closed loop paint circulation system provides continuously circulating paint between a paint reservoir and a paint applicator for use in a production paint facility. A circulation line fluidly communicates the paint at a desired operational pressure between the paint reservoir and the paint applicator. A relief line is cooperably seperable from the circulation line by a relief device that opens for reducing the operational pressure of the paint circulating through the circulation line when the operational pressure increases beyond a predetermined value. A secondary pressure relief device is cooperable with the first pressure relief device where the second pressure relief device actuates in response to a difference between the predetermined pressure and the operational pressure to prevent the first relief device from opening.

The first pressure relief device, generally a rupture disc, as stated above, requires a significant amount of maintenance upon opening, i.e., rupturing, to prevent pressure buildup within the paint circulation line from causing damage to the paint circulation pump and various seals. Providing a second pressure relief device that opens at a pressure just below the predetermined pressure that causes the rupture disc to rupture allows pressure relief to be introduced to the paint circulation system without the requisite maintenance and the associated manufacturing down time set forth above.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

FIG. 1 is a schematic view of an inventive paint circulation system for supplying paint to a paint applicator and an associated pressure control device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, wherein like numerals indicate like or corresponding parts, an inventive closed loop paint circulation system is generally shown at 10. The paint circulation system 10 supplies paint to at least one paint booth 12 where the paint is applied to a product, such as, for example, a vehicle body 14. In a typical automobile assembly plant paint is maintained in constant circulation through long circulation line 16 stretching between a paint reservoir 18 and one or more paint spray booths 12 by a pump 20. The vehicle body 14 is transported through the paint spray booth 12 by conveying equipment (not shown) where the paint is applied to the vehicle body 14 and subsequently cured in a paint oven (not shown) as is known to those skilled in the art. The paint may be applied by human operators or mechanically by automated equipment 22 such as rotary atomizers. The equipment 22 is generally disposed inside the walls of the paint booth 12 and is robotically operated, as again, is known to those skilled in the art.

The circulation line 16 fluidly communicates with the paint reservoir 18 defining a first fluid circulation circuit, generally indicated at 24, wherein the paint is circulated at a generally constant pressure, i.e. operational flow pressure. Various manually operated valves 26 are disposed in the circulation line 16 as will be described further below. These valves 26 are generally closed during maintenance operations. The pump 20 is located downstream of the paint reservoir 18 and provides circulation pressure to the paint circulation system 10 by delivering the paint from the paint reservoir 18. Those skilled in the art will appreciate that various types of pumps may be used with present inventive concept and which do not limit the inventive concept.

A relief line of the present invention is generally indicated at 28. The relief line 28 fluidly communicates with the circulation line 16 and is separable by a pressure relief device, such as, for example a rupture disc 30. The rupture disc 30 ruptures or opens when the operational flow pressure of the paint circulating through the circulation line 16 increases beyond a predetermined value. Typically, if a vessel's internal pressure rises to the predetermined value, the rupture disc 30 bursts, providing an instantaneous, unobstructed full relief by allowing the paint to circulate through the relief line 28. Preferably, the rupture disc 30 is certified for 300 PSI or other predetermined value known to prevent damage to the paint circulation system 10. A sight tube 32 is disposed in the relief line 28 to provide verification that the rupture disc 30 is opened or as the paint is circulating through the relief line 28.

A second pressure relief mechanism is cooperable with the rupture disc 30 and operates in response to the difference between the predetermined flow pressure and the operational flow pressure thereby preventing the rupture disc 30 from opening or rupturing. The second pressure relief mechanism includes a pressure control sensor/transmitter 34 for sensing the differences in the operational flow pressure preferably located between the pump 20 and the first of the valves 26 positioned downstream of the pump 20. A pressure relief valve 36 of the second pressure relief mechanism is fluidly communicated with the relief line 28 and is operated in response to the pressure control sensor/transmitter 34. Preferably, the pressure relief valve 36 is 1½″ stainless steel three pieces pneumatically actuated pressure relief ball valve located in a tee branch downstream of the pump 20. Other types of mechanical valves known to those skilled in the art and may be used as desired and should not limit the inventive concept.

As further illustrated in FIG. 1, an actuating device is cooperable with the pressure relief valve 36 for operating the pressure relief valve 36 in the second pressure relief device in response to pressure difference between the operational flow pressure and the predetermined flow pressure. The actuating device includes an actuator 40 for pneumatically opening and closing the pressure relief valve 36 and a solenoid valve 42 for energizing the actuator 40. The actuator 40 is designed to hold the pressure relief valve 36 in a closed position by generally 40 PSI of compressed air. Those skilled in the pneumatic art will appreciate that various additional sources of compressed air may be fluidly communicated with the inventive system 10. Furthermore, sensor actuated valves may also be used to adjust response time if required. Preferably, the solenoid valve 42 is rated for explosion proof use and is designed for continuous operation at 24 volt DC. A pressure regulator 44 is cooperable with the actuator 40 for regulating amount of pressure supplied from one of the aforementioned sources of compresses air that normally supplies compressed air at 90 PSI.

Generally, two of the manually operated valves 26 are disposed in the circulation line 16 on opposite sides in a given components, such as a filter bag 46. These valves 26 are designed to shut down flow of the paint in case of emergency, maintenance, such as, changing a filter bag 46, positioned downstream the relief line 28. A back pressure regulator 48 is disposed at the circulation line 16 to monitor the operational flow pressure required for circulating the paint in the circulation line 16 and for maintaining the operational flow restrictions. Those skilled in the art will appreciate that various types of the back pressure regulator 48 may be used with present inventive concept and which do not limit the inventive concept.

A controller 50 is operably connected to the pressure control sensor/transmitter 34 and the solenoid valve 42. Preferably, the controller 50 includes a computer having an input/output interface, a central processor unit, a random access memory, i.e. RAM, and a read only memory, i.e. ROM. The input interface is electrically connected with the pressure control sensor/transmitter 34 and the solenoid valve 42 for operating the second pressure relief mechanism in response to the difference between the operational flow pressure and the predetermined flow pressure before the operational flow pressure exceeds the predetermined flow pressure to prevent the rupture disc 30 from opening. Preferably, the flow pressure that initiates the opening sequence for the pressure relief valve 36 is far enough below the predetermined flow pressure that opens the rupture disc 30 to allow enough time for the controller 50 to open the pressure relief valve 36.

In a normal operating mode of the paint circulation system 10, the paint is circulated through the circulation line 16 under the operational flow pressure of approximately 200 PSI and is delivered to the paint applicator 22 disposed in the paint booth 12 to be applied to the vehicle body 14. When the operational flow pressure exceeds 200 PSI due to an inadvertent pressure relief valve 36 closure or if the paint circulation system 10 becomes blocked, and before the operational flow pressure reaches the predetermined flow pressure of, for example 300 PSI, the pressure sensor/transmitter 34 will detect a high flow pressure conditions to either speed-up or slow down the pump 20. For example, if the operational flow pressure exceeds but before the operational flow pressure reaches the predetermined flow pressure, the pressure sensor/transmitter 34 will detect the difference in the operational flow pressure thereby signaling the controller 50 this difference. The controller 50 then signals the solenoid valve 42 that is operatively connected to the pressure relief valve 36. The solenoid valve 42 is de-energized through the signal received from the controller 50 as the pressure sensor/transmitter 34 responds to the difference between the predetermined flow pressure and the operational flow pressure in the paint circulation system 10. The solenoid valve 42 cooperable with the actuator 40 assists the actuator 40 thereby venting out compressed air from the actuator 40 cooperable with the pressure relief valve 36. The loss of compressed air pressure operates as the actuator spring return to mechanically open the pressure relief valve 36 to allow the paint circulation in the relief line 28. The pressure relief valve 36 is opened as soon as the operational flow pressure exceeds its operational value but before the operational flow pressure reaches the predetermined flow pressure. An alarm (not shown) is operatively communicated with the circulation line 16 and is actuated to warn maintenance crew about the inadvertent valve closure or if the paint circulation system 10 becomes blocked. The alarm is actuated as soon as the pressure relief valve 36 is opened in response to the difference between the operational flow pressure and the predetermined flow pressure.

While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A closed loop circulation system for providing paint to a paint applicator comprising; a circulation line fluidly communicating with the paint applicator thereby providing paint at an operational pressure to the paint applicator, a relief line separable from said circulation line by a pressure relief device for reducing the operational pressure of the paint circulating through said circulation line when the operational pressure inside said circulation line increases beyond a predetermined value, and a second pressure relief device cooperable with said first pressure relief device wherein said second pressure relief device actuates in response to a difference between a second predetermined pressure and the operational pressure thereby preventing said first pressure relief device from actuating.
 2. A closed loop circulation system as set forth in claim 1, including a controller operatively communicating with said second pressure relief device for actuating said second pressure relief device as the operational pressure exceeds the second predetermined pressure.
 3. A closed loop circulation system as set forth in claim 2, wherein said second pressure relief includes a pressure control sensor for sensing differences in the operational pressure with said pressure control sensor operatively communicated with said circulation line.
 4. A closed loop circulation system as set forth in claim 3, wherein said second pressure relief includes a valve fluidly communicated with said relief line and operatively communicated with said pressure control sensor for continuously circulating the paint in said relief line before the operational pressure exceeds the predetermined pressure.
 5. A closed loop circulation system as set forth in claim 4, wherein said valve is a ball valve.
 6. A closed loop circulation system as set forth in claim 5, including an actuating device cooperable with said valve for activating when signaled by said controller.
 7. A closed loop circulation system as set forth in claim 6, wherein said actuating device includes an actuator for pneumatically opening and closing said valve and a solenoid valve for energizing said actuator, said solenoid valve and said actuator presenting an operative communication with said controller.
 8. A closed loop circulation system as set forth in claim 7, including a pressure regulator cooperable with said actuator for regulating amount of air pressure supplied to said actuator.
 9. A closed loop circulation system as set forth in claim 8, wherein said pressure relief device comprises a rupture disc.
 10. A closed loop circulation system as set forth in claim 9, including a sight tube fluidly communicated with and disposed in said relief line thereby allowing visible verification that said the paint being circulated through said relief line.
 11. A closed loop circulation system as set forth in claim 10, wherein said relief line is disposed upstream in said circulation line from a first valve disposed in said circulation line.
 12. A closed loop circulation system as set forth in claim 1, including a paint supply source fluidly communicating with said circulation line for storing the paint.
 13. A closed loop circulation system as set forth in claim 1, including a pump for pumping the paint delivered from said paint supply source at the operational pressure.
 14. A closed loop circulation system as set forth in claim 1, including at least one paint booth cooperable with said circulation line.
 15. A paint circulation system for coating applications having a paint supply source and a pump for pumping paint, said paint circulation system comprising: a circulation line fluidly communicating with the source of paint supply for circulating the paint at an operational pressure; a relief line having a pressure relief device adaptable for withstanding a predetermined pressure being higher than the operational pressure and for circulating the paint through said relief line as the operational pressure exceeds the predetermined pressure; and a pressure control mechanism operatively communicated with said circulation line and said relief line for sensing the operational pressure and for continuously circulating the paint in said relief line in response to a difference between the operational pressure and a second predetermined pressure before the operational pressure exceeds the predetermined pressure thereby preventing said pressure relief device from actuating.
 16. A paint circulation system as set forth in claim 15, wherein said second pressure relief includes a pressure control sensor for sensing differences in the operational pressure with said pressure control sensor operatively communicated with said circulation line.
 17. A paint circulation system as set forth in claim 16, wherein said second pressure relief includes a valve fluidly communicated with said relief line and operatively communicated with said pressure control sensor for continuously circulating the paint in said relief line as said pressure control sensor signals difference between the operational pressure and the predetermined pressure before the operational pressure exceeds the predetermined pressure.
 18. A paint circulation system as set forth in claim 17, including a controller operatively communicated with said second pressure relief device for activating said second pressure relief device as the operational pressure exceeds.
 19. A paint circulation system as set forth in claim 18, including an actuating device cooperable with said valve for operating said valve in different operational modes of said second pressure relief device.
 20. A paint circulation system as set forth in claim 19, wherein said actuating device includes an actuator for pneumatically opening and closing said valve and a solenoid valve for energizing said actuator, said solenoid valve and said actuator presenting an operative communication with said controller.
 21. A paint circulation system as set forth in claim 20, including a pressure regulator cooperable with said actuator for regulating amount of pressure supplied to said actuator.
 22. A paint circulation system as set forth in claim 21, wherein said relief line is disposed in said circulation line upstream from a first valve disposed in said circulation line.
 23. A paint circulation system for coating applications having a paint supply source and a pump for pumping paint, said paint circulation system comprising: a circulation line for fluidly communicating with the source of paint supply and circulating the paint at an operational pressure; a relief line having a pressure relief device adaptable for withstanding a predetermined pressure being higher than the operational pressure and for circulating the paint through said relief line as the operational pressure exceeds the predetermined pressure; and a pressure control sensor for sensing differences in the operational pressure operatively communicated with said circulation line and said relief line and a valve fluidly communicated with said relief line and operatively communicated with said circulation system for continuously circulating the paint in said relief line as said pressure control sensor signals difference between the operational pressure and the predetermined pressure before the operational pressure reaches the predetermined pressure thereby preventing said pressure relief device from actuating.
 24. A paint circulation system as set forth in claim 23, including a controller operatively communicated with said second pressure relief device for actuating said second pressure relief device as the operational pressure exceeds.
 25. A paint circulation system as set forth in claim 24, including an actuating device cooperable with said valve for operating said valve in different operational modes of said second pressure relief device.
 26. A paint circulation system as set forth in claim 25, wherein said actuating device includes an actuator for pneumatically opening and closing said valve and a solenoid valve for energizing said actuator, said solenoid valve and said actuator presenting an operative communication with said controller.
 27. A paint circulation system as set forth in claim 26, including a pressure regulator cooperable with said actuator for regulating amount of pressure supplied to said actuator.
 28. A paint circulation system as set forth in claim 27, including a first valve valves fluidly communicated with said circulation line and disposed downstream of said pressure control sensor.
 29. A paint circulation system as set forth in claim 28, including a filter fluidly communicated with and disposed on said circulation line, said fluid filter positioned downstream said relief line and said first valve. 